Ticket #26850: 26850.4.diff

src/wp-includes/formatting.php

@@ -108 +108 @@
                         $dynamic[ '/(?<=\A|' . $spaces . ')\'(\d[\d\.\,]*)\'/' ] = $opening_single_quote . '$1' . $closing_single_quote;
                 }
 
-                // '99 '99s '99's (apostrophe)
+                // '99 '99s '99's (apostrophe)  But never '9 or '999.
                 if ( "'" !== $apos ) {
-                        $dynamic[ '/\'(?=\d)/' ] = $apos;
+                        $dynamic[ '/\'(?=\d\d(\D|\Z))/' ] = $apos;
                 }
 
                 // Single quote at start, or preceded by (, {, <, [, ", -, or spaces.